Hi Brad,
Ask not what you can do to maximise your SEO, but what can you do to make your user experience better.
In other words ensure that your visitor gets all the info he/she needs.
1. Make sure you link to products in the Video Description so anyone watching can easy find and purchase.
2. Have you considered creating a transcript to go along with the video?
3. Are the videos embedded on your product pages?
4. Have you shared the videos with your social circles?
5. Are the videos correctly branded with your website logo and URL? alot can change in a few years is the branding the same as it was when the videos were produced?
6. Have you considered creating some new videos? You channel may or may not have subscribers who could come back and view your new videos and maybe purchase a product or two.
These are just my initial thoughs on what I would consider doing, I'm sure you have already touched upon these.
Cheers
Aran

